After Stacey Hanson, a private investigator, spends the morning racing cars at the Riverside Raceway, she visits her boyfriend, Bob Eastwood, on his yacht, where she receives a letter with a job offer. Stacey drives to a mansion in Bel-Air, California, where she meets Florence Chambers, a wealthy, elderly woman in a wheelchair who hires her to investigate the possible heirs to her fortune. Florence uses a bullhorn to call her assistant, Frank Shaw, interrupting a tryst he is having with Tish Chambers, the wife of Florence’s grandnephew John Chambers. Later, Florence introduces Tish, Frank, John and Marian, the maid, to Stacey, claiming the detective is the granddaughter of old friend. As they sit for dinner, Pamela Chambers, Florence’s free-spirited grandniece and John’s sister, arrives and trades insults with Tish and John. That night, Stacey is undressed when Frank enters her room and offers to sleep with her. She knees him in the groin and forces him to leave. The next day, Frank surreptitiously photographs Tish as they have sex at the family beach house. Meanwhile, Stacey volunteers to drive Pamela to visit Rodney Clark, a friend of Pamela’s who lives in Palm Springs. They arrive to find a house full of older men and young women engaging in drug use and sex. Pamela gives Rodney Clark a roll of money and introduces Stacey. Two of Clark’s friends, Matthew and Luke, arrive and Matthew kisses Stacey on the chest as a way of greeting. She smashes a bottle and threatens to cut him with the jagged glass if he tries it again. Clark apologizes for his friend’s behavior and takes the broken bottle away from Stacey. That night, Frank Shaw gets a telephone call from Dick, a mobster, who demands he pay back a loan. Frank hangs up and shows Tish the revealing pictures he took. She reproaches him and leaves. Later, Frank attempts to blackmail John with the photographs, but John is indifferent until Frank produces photographs of he and John in bed together. The next night, Florence throws a party at her home where Frank is distressed to find the mobster, Dick, pretending to be a bartender. He telephones John, but again John refuses to give in to blackmail. When Frank hangs up, Dick jumps out of the shadows and cuts Frank’s face with a switchblade, threatening worse if he is not paid soon. After the party, Frank returns to his room, and is attacked by a knife-wielding assailant. Although stabbed multiple times, he is able to snap a photograph of his killer before dying. The next morning, Stacey finds Frank’s body by the pool. After calling Florence and John, she follows a trail of blood back to Frank’s room and finds Tish. Ordering her out, Stacey searches the room, discovers a camera, removes the film and hides it in her towel, unaware that Marian is watching through the window. Later, police Lt. Brodsky, an old friend of Stacey’s, arrives to investigate the murder and Marian hands him an envelope containing the photographs of Frank and Tish. After the police leave, Marian makes a telephone call and informs the other party that Stacey is going to the beach house. Meanwhile, Stacey and Bob Eastwood find the beach house and make love. During their amorous activities, Stacey reaches under the bed and finds Frank’s shutter release cable. A quick search reveals the camera hidden behind a mirror. Outside, two men drive up and when Bob comes out to smoke, they club him unconscious. Entering the house, the men hear the shower running. One of the men pulls back the shower curtain to find Stacey fully clothed with her gun drawn. She shoots the man between the eyes, then runs outside and kills the other in a gun battle. Fearing that Aunt Florence Chambers may have sent the men after her, Stacey orders Bob to hide the dead men’s car and then meet her at his yacht. Later, Matthew and Luke appear at the marina and sneak on the boat carrying shotguns. Stacey wakes up and opens fires with her pistol. As Stacey and Bob chase Luke, Matthew doubles back and searches Bob’s boat. Unable to find anything, he and his partner drive away. In the morning, Bob drives to the Riverside Raceway to ask a photographer friend to develop Frank’s film. After seeing the photographs, Bob telephones Stacey, unaware that Marian is listening in on another extension. Stacey arrives at the racetrack and views photographs of Frank sleeping not only with Tish and John, but also with Marian. Stacey looks at Frank’s last photography and tells Bob they have to see Florence Chambers immediately. In the parking lot, Matthew and Luke appear with shotguns and shoot Bob as he pushes Stacey to safety. A running gun battle erupts with various bystanders shot and killed. Stacey makes it to her car, but Luke shoots out her tires. She leaps into a nearby racecar and speeds away. Matthew and Luke hijack a helicopter and give chase. Matthew orders the pilot to land in front of the car, but when the two thugs jump out, Stacey drives by and hits Luke. She stops to see if Luke is dead, but cannot get the racecar started again. She runs and hides as Matthew and a limping Luke chase her. Stacey shoots Luke dead, recovers his shotgun, then kills Matthew. She hitchhikes back to Palm Springs and goes to Rodney Clark’s house to find an orgy in progress. She shoots a record player and demands everyone but Pamela and Rodney leave. When Brodsky, Bob and the police arrive, Stacey shows them Frank’s last photograph, which clearly shows Pamela Chambers wearing a nylon mask. Later, Stacey and Bob explain to Florence that Rodney was running a cult and getting his members to blackmail wealthy targets. When Frank failed to blackmail John or Tish, he ordered Pamela to kill him. Rodney had then planned for Marian to kill John and Florence, allowing Pamela to inherit the family fortune and turn it over to his cult. After their meeting, Stacey surprises Bob with a boat a cruise to Mexico.